High-pressure gas discharge lamp

Abstract

A high-pressure gas discharge lamp (HID [high intensity discharge] lamp) is described which is designed in particular so as to be free from mercury and suitable for use in automobile technology. To achieve improved lamp properties, in particular a substantially equal luminous efficacy compared with lamps of the same power and having a gas filling with mercury, as well as a burning voltage which is as high as possible, a geometry is proposed for the discharge space ( 2 ) which raises the temperature of the coldest spot in the lamp to such a degree that the light-generating substances can enter the gas phase to a sufficient extent also without mercury, and in particular in combination with the use of a metal halide as a voltage gradient generator.

What is claimed is:  
     
       1. A high pressure discharge lamp with a discharge vessel which encloses a discharge space with a light-generating substance and with a bottom surface which is in lowermost position in the operational position of the lamp, which bottom surface has a raised region and recessed regions, the discharge space having a long dimension and the discharge vessel having an exterior surface wherein; 
       the bottom surface of the discharge space is curved along the long dimension, said raised region being near the center of said long dimension and said recessed regions being near the ends of the long dimension of the discharge space, and said discharge space further being enclosed by a top surface opposite said bottom surface, which is planar.  
     
     
       2. A high-pressure gas discharge lamp as claimed in  claim 1 , comprising pinches ( 5 ) which are arranged symmetrically with respect to the discharge vessel ( 1 ). 
     
     
       3. A high-pressure gas discharge lamp as claimed in  claim 1 , comprising a gas filling which is free from mercury. 
     
     
       4. A high-pressure gas discharge lamp as claimed in  claim 3 , which comprises a voltage gradient generator in the form of one or several metal halides in its gas filling. 
     
     
       5. A high-pressure gas discharge lamp as claimed in  claim 4 , wherein the voltage gradient generator comprises zinc iodide. 
     
     
       6. A high-pressure gas discharge lamp as claimed in  claim 3 , wherein the gas filling comprises quantities of rare gases, for raising the gas pressure and for enhancing the luminous efficacy of the lamp. 
     
     
       7. A high-pressure gas discharge lamp as claimed in  claim 1 , wherein the outer wall of the discharge vessel ( 1 ) opposed to the raised region of the bottom surface ( 11 ) is provided with a coating which comprises zirconium oxide (ZrO 2 ). 
     
     
       8. A high-pressure gas discharge lamp as claimed in  claim 1 , wherein the lamp has electrodes and pinches and wherein the outer wall of the discharge vessel ( 1 ) is provided with a coating comprising zirconium oxide (ZrO 2 ) in regions of entry locations ( 7 ) of at least one of the electrodes ( 3 ) and the pinches ( 5 ). 
     
     
       9. A lighting unit, in particular for motor vehicle headlights, with a high-pressure gas discharge lamp as claimed in  claim 1 . 
     
     
       10. A high-pressure gas discharge lamp as claimed in  claim 1 , said discharge space further being such that its shape in a plane perpendicular to the long dimension at the center of the long dimension is circular except for a straight line portion at the location of said bottom surface. 
     
     
       11. A high-pressure gas discharge lamp as claimed in  claim 10 , wherein the shape of said exterior surface of the discharge vessel at a bottom region is congruent with the shape of said bottom surface. 
     
     
       12. A high pressure discharge lamp with a discharge vessel which encloses a discharge space with a light-generating substance and with a bottom surface which is in lowermost position in the operational position of the lamp, which bottom surface has a raised region and recessed regions, the discharge space having a first long dimension and the discharge vessel having an exterior surface wherein; 
       the bottom surface of the discharge space is curved along a second dimension perpendicular to the long dimension, said raised region being near the center of said second dimension and said recessed regions being near the ends of said second dimension.  
     
     
       13. A high-pressure discharge lamp as claimed in  claim 12 , wherein the shape of the discharge vessel at a bottom region is congruent with the bottom of the discharge space.